1. Field of the Invention
This invention relates to a detergent composition for removing stains of oils and fats, machine oils, cutting oils, grease, liquid crystals, rosin-type fluxes, and the like attached to the solid surfaces of articles such as electronic and precision parts, and tools used for the assembly or fabrication of these parts (such parts and tools herein collectively called "electronic and precision parts"), and to a process for cleaning the electronic and precision parts using said detergent composition, which is characterized by the ease in treating the waste water discharged therefrom.
2. Description of the Background Art
Conventionally, hydrocarbon solvents, e.g. kerosene, benzene, xylene, etc.; chlorine-containing solvents, e.g. trichloroethylene, tetrachloroethylene, etc., Freon-type solvents, e.g. trichlorotrifluoroethane, etc.; aqueous type detergents comprising surface active agents, builders, etc.; and the like have been used for removing stains, of which the major components are oils and fats, machine oils, cutting oils, greases, liquid crystals, rosin-type fluxes, and the like, attached to the solid surfaces of precision parts and tools. In particular, Freon-type solvents and chlorine-containing solvents are used for removing stains on electronic, electrical, and machinery parts owing to their high detergency and flame retardance.
The detergent compositions containing a chlorine-containing solvent or a Freon-type solvent, however, have crucial problems in terms of the safety, toxicity, environmental pollution, and the like. Among hydrocarbon solvents, benzene and xylene are both specified as hazardous compounds under the Law Concerning Industrial Hygiene and Workmen's Safety because of their high toxicity, and are therefore undesirable solvents for use in a detergent composition. Special consideration must be given to avoid risks involved in handling these solvents.
Aqueous type detergents, on the other hand, are less hazardous and toxic than solvent type detergents. High detergency can be provided by properly selecting detergent components such as surface active agents, builders, and the like.
Aqueous type detergents containing various types of surface active agents are usually abundantly soluble in water. This is the cause of the drawback of these aqueous type detergents; i.e. difficulty in the treatment of waste water. The treatment of a detergent liquid after removing stains and the treatment of the waste water used to rinse the detergent liquid from the parts to be cleaned (such waste water herein called "rinse waste water") have conventionally been carried out by coagulation and sedimentation, pressure flotation, activated sludge treatment, or activated carbon treatment, or by the combination of two or more of these. These treatment processes, however, require large facilities involving enormous investment and operating costs.
The object of the present invention is therefore, with due consideration to the above problems and drawbacks in aqueous-type detergent compositions or the detergent composition of the type in which water is used for the rinse after washing, to provide a detergent composition of which the rinse waste water can easily be treated and which can effectively remove stains of oils and fats, machine oils, cutting oils, greases, liquid crystals, rosin-type fluxes, and the like from the solid surfaces of electronic and precision parts. Another object of the present invention is to provide an industrially advantageous process for cleaning electronic and precision parts without requiring large facilities involving huge investment cost and high operating costs.
The present inventors have undertaken extensive studies and have found that the above objects can be achieved by a detergent composition comprising, as a detergent ingredient, one or more nonionic surface active agents, of which a 5% by weight aqueous solution has a cloud point of 5.degree.-100.degree. C.
The present inventors have further found that the rinse waste water after cleaning the electronic and precision parts with the detergent composition and after rinsing at a temperature of 5.degree.-100.degree. C. can easily separate out the oil components contained therein, such as oil stains and detergent components, if heated to a temperature above the cloud point, thereby remarkably improving the waste water treatment process and ensuring recycling of the rinse water from which the oil components have been eliminated.